Unlike 123I which is a gamma emitting isotope 124I, a positron emitter, with a half-life of 4.2 d, can be used for positron emission tomography (PET) thus allowing a better as well as quantification of tracer accumulation Studies using 124I-MIBG positron emission tomography was initiated as early as 1992. Preliminary studies demonstrated that imaging with 124I-MIBG in humans is safe when using the correct amount of radioactivity tracer.